A missing number in this mailer cost Macy's a whole lot of money, and a PR headache. Image courtesy: KVDR.com

Typos really don't matter. Yes, you read that right. I am a professional proofreader and I confess: For the most part, typos don't make or break a sale or bankrupt a company. They don't turn off new clients and really don't affect a company's bottom line. In fact, most people don't notice typos. It's grammar police like me who care. We relish at finding errors (and pointing them out with our red pen to the rest of the world).

But there are instances where one tiny mistake can absolutely KILL your credibility, make your customers run to your competitors and cost you thousands of dollars. Take for instance the Macy's mailer that incorrectly stated a $1,500 necklace was on sale for only $47 (see image above). Now, I'm not one who wears flashy jewelry, but that's one choker I'd love to have.

As you can see, a single letter, or in this case, number, can cost a well-known department store lots of money, not to mention the time and energy to repair the damage to its reputation. When typos strike, they are disastrous to your credibility and future sales.

So how do you know when typos are going to affect your business? How do you know whether you should hire a professional proofreader instead of relying on Aunt Bettie or the co-worker with the English degree?

Here are three main considerations when determining the repercussions of typos:

1) Prominence. In a short blog post, a mistake midway down or at the end probably won't get much attention from the general public. But you can be sure an error in the headline will get your phone ringing off the hook. The first thing readers see becomes the deciding moment for your sales and credibility. Think banners, storefront signs, advertisements, emblems, billboards, posters, sandwich boards, even the subject line of your emails. Proofreading is always done with special attention to the top. The City of South Bend, Ind., found out the hard way after posting a huge highway sign with an embarrassing typo (see image below).

2) Frequency. A (classic) typo like "it's/its" may not be a big deal to some people, but when your story, article or text is riddled with errors all the way through, your reader will get turned off and most likely never come back to your website or blog. An outside source who employs proven techniques is your best route to clean, error-free publicity.

Drivers in Indiana got a glimpse of this classic and unfortunate typo. Image courtesy: The Guardian.

A trained proofer uses methods like reviewing from the bottom to the top and reading out of context. I honed this skill while working on Wall Street for 10 years proofreading financial newsletters and reports for institutional clients. The stakes were high because mistakes had a ripple effect, often turning off clients for the long term.

"When typos strike, they are disastrous to your credibility and future sales."

This broadcast journalist was mislabelled during her stand-up in front of the White House. Image courtesy: MSNBC.

Misspellings on headstones and monuments are not only embarrassing but costly. Image courtesy: oddlovescompany

3) Situation. Are you sending a note about a party, writing an obituary for a loved one or emailing 10,000 customers pitching your latest product? Context plays an important role in proofreading.

In other words, that quick email to a handful of your friends where you misspell "cocktail" as "cooktail" might get a giggle, but imagine a thousand-dollar engraved marble headstone with a mistake like this one. The person who did the proofreading (or failed to do so) is probably out of a job. More importantly, the family of the deceased is understandably fuming and, on top of it, heartbroken to be reminded every time they visit the cemetery.

Furthermore, the headstone company might get panned through negative reviews. So remember, a mistake that seems to affect only one customer gets magnified in today's online world. ​When it comes to corrections, these important considerations will help you decide on your budget for a professional. The time and money you invest in high-level proofreading (no offense to Aunt Bettie) will help you avoid PR gaffes and embarrassing mistakes. More importantly, it will reap rewards to your bottom line. ​

Jennifer Karchmer is a professional proofreader, grammar guru and spelling bee champion (8th grade). She worked as an editor and proofreader on Wall Street and currently offers clients worldwide proofreading solutions. She holds a master's degree in communications.